The present invention relates to a fuel pressure control system, and more specifically to a system for controlling a fuel pressure regulator.
Japanese Utility Model application, provisional publication number 55-94436 discloses one example of the conventional fuel pressure control system. As shown in FIG. 1, this system has a fuel pressure regulator 3 disposed in a fuel feed passage extending from a fuel pump 1 to a fuel injector 2. The pressure regulator 3 has a fuel chamber 5 and a reference pressure chamber 6 which are separated by a diaphragm 4. A return passage 7 for returning the fuel from the fuel chamber 5 to a fuel tank has an open end located in the fuel chamber 5. The diaphragm 4 opens and closes the return passage 7 by deflecting in accordance with the intake manifold vacuum introduced into the reference chamber 6. Thus, the fuel pressure regulator 3 can control the fuel pressure so that a pressure difference between the fuel pressure and the intake vacuum can be maintained constant (2.5 kg/cm.sup.2, for example). Therefore, the fuel pressure is given by;
Fuel pressure (kg/cm.sup.2)=2.5+Reference pressure of Regulator
During idling, the reference pressure is negative, and therefore the fuel pressure is smaller than 2.5 kg/cm.sup.2. When the reference pressure is equal to atmosphere pressure (the reference pressure=0), the fuel pressure is maintained equal to 2.5 kg/cm.sup.2.
A control valve 9 is disposed in a reference pressure passage 8 conveying the intake manifold vacuum to the reference chamber 6. When a hot start sensor (temperature sensor) 10 detect that the fuel temperature is high, the control valve 9 introduces atmospheric pressure into the reference chamber 6 to prevent vapor lock by increasing the fuel pressure.
However, this system cannot increase the fuel pressure sufficiently to prevent vapor lock, so that there remains a possibility that vapor of fuel decrease and increase the fuel supply violently, and causes engine troubles such as difficulty in starting engine and fluctuation of engine rotational speed.